The present invention relates generally to disposable electrodes, and more particularly to a skin contact electrode assembly for detecting cardiac and other low level electrical signals generated within the human body.
Skin contact electrodes find extensive use for detecting and transforming potentials generated within the body into electrical signals which may be monitored for a variety of functions, such as the preparation of electrocardiograms and electroencephalograms. Originally, such electrodes were of the permanent or non-disposable type wherein a metal electrode was placed in contact with the skin with an interposed layer of electrolyte, generally in gel form. Not only was the placing of the electrode, which often had to be strapped to the patient, cumbersome and inconvenient, but the application of the gel electrolyte had to be done very carefully to avoid contact with the clothes of the patient and the person conducting the test. In addition, the electrodes had to be cleaned after each use for reasons of sanitation and to insure a good electrical contact.
In recent years, with the advent of portable and more sophisticated EKG and other types of biomedical monitoring equipment, disposable electrode assemblies, wherein the metallic electrode and the electrolyte gel, together with an adhesive for holding the electrode in position, are combined in a unitary assembly for one-time use, have come into wide use. Not only do these assemblies avoid the time-consuming processes of applying gel and strapping the electrode in position, but they also avoid the necessity of cleaning the electrode after each use.
Unfortunately, prior art disposable type electrode assemblies have not been entirely satisfactory in all respects. Typically, such electrode assemblies have used thin paper or plastic adhesive-backed base members to which the electrode was attached, and a cover member for covering the adhesive until ready for use. Because the base and cover members provided little or no stiffness to the assemblies, the assemblies were difficult to store and difficult to prepare for use. Furthermore, the elements of the assembly were often torn or damaged in attempting to remove the cover member prior to use, and the user was often subjected to undesired contact with either the electrolyte gel or the adhesive.
The lack of stiffness in prior art electrode assemblies also precluded stacking of the assemblies while in storage, making it necessary to package each assembly in an individually sealed package suitable for storage in a drawer or open box. This not only unnecessarily consumed the time of the user by requiring him to unwrap each package separately prior to use, but also unnecessarily increased the cost of the electrode assemblies. Attempts at placing more than one electrode assembly in a package proved unsatisfactory because the number of electrodes required for a particular situation varied, resulting in the unwrapping and discarding of unneeded electrodes. Accordingly, the need has developed for a disposable electrode assembly which can be conveniently stored and dispensed in a desired quantity with no waste or damage to unused electrodes.
Those assemblies which utilized a thicker or stiffer base member in attempting to overcome these deficiencies tended to separate from the skin after a period of time, and often caused discomfort to the patient during extended monitoring periods. Use of a stronger adhesive to hold the stiffer base members in position aggravated the discomfort of the patient as the electrodes were removed or repositioned. The use of a stiffer base member in prior art electrode assemblies also increased the possibility of spurious output signals being produced as the patient moved. Such motion artifacts resulted from mechanical disturbance of the electrolyte relative to the metal electrode, which was aggravated by the use of a stiff base member above the skin contact area.
Occasionally skin contact electrodes are utilized in a continuing monitoring process where it is necessary to leave the electrodes in position over an extended period of time, for days or even weeks. In this situation, it is desirable to periodically monitor the condition of the patient's skin under the electrode assembly for possible irritation. With prior art electrode assemblies it was necessary to periodically peel the assembly at least partially away from the skin for this purpose, thereby increasing the likelihood of the skin becoming irritated and the adhesion capabilities of the adhesive being weakened. Thus, the need exists for a disposable electrode assembly which allows skin condition to be monitored without disturbing the electrode.
In addition to the aforementioned attributes of convenience of storage and use, it is necessary that a body electrode assembly of the disposable type be economical to manufacture and package. To this end the materials employed in its manufacture must be readily obtainable and the individual components utilized in the assembly must be capable of fabrication by efficient techniques and processes. It is to a new and improved disposable electrode assembly which combines the desired economy of construction and convenience of packaging with low contact resistance, good adhesion and low motion artifacts, that the present invention is directed.